FIG. 1 is a schematic view of a conventional lens module. Referring to FIG. 1, the conventional lens module 100 includes a lens 110 and a focus wheel 120. The focus wheel 120 can be rotated in a clockwise direction or a counter-clockwise direction, so that the lens 110 can be moved forward or backward along a predetermined direction E1 to achieve the purpose of focusing. However, the above focus control mode is a manual focus control mode and the use of the lens module 100 is inconvenient.
FIG. 2A is a schematic view of another conventional lens module. FIG. 2B is an exploded schematic view of the lens module of FIG. 2A. Referring to FIGS. 2A and 2B, Taiwan Publication Patent No. 201011366 has disclosed the lens module 20. The lens module 20 includes an outer lens barrel 210, an inner lens barrel 220 and a lens 230. The outer lens barrel 210 has a guide slot 212 and a cam groove 213. The inner lens barrel 220 has a cam pole 221 and a restricting slot 223 corresponding to the cam groove 213. The lens 230 is disposed in the inner lens barrel 220. In the lens module 20, the lens 230 is moved by the outer lens barrel 210 cooperative with the inner lens barrel 220 to achieve the purpose of focusing. However, the above focus control mode is also the manual focus control mode and the use of the lens module 20 is inconvenient.
FIG. 3 is a schematic view of another conventional lens module. The conventional lens module 300 includes a lens 310, a motor 320, a screw 330 and two rods 340. The lens 310 is coupled with the two rods 340, so that the lens 310 can be moved along the two rods 340. The motor 320 is used to drive the screw 330 to rotate, and the lens 310 is further coupled with the screw 330. When the screw 330 is rotated in a clockwise direction or a counter-clockwise direction by the motor 320, the screw 330 can move the lens 310 forward or backward along a predetermined direction E2 to achieve the purpose of focusing.
In comparison with the manual focus control mode, the lens module 300 can be used conveniently due to its automatic focus control mode. However, when the lens module 300 is focused, an actual position can not be determined, and the lens 310 is easily to be moved beyond safe limit. As such, the lens 310 may impact other components, so the lens 310 and the motor 320 are easily damaged.
For overcoming the above shortcomings, the lens module 300 can further include a sensor to sense the actual position of the lens 310. However, the use of the sensor would increase the volume and cost of the lens module 300. Furthermore, the sensor may have the shortcomings of low sensitivity and accuracy, and therefore the production yield and reliability of the lens module 300 would be decreased.